This invention relates to a damage detecting device for a laser power transmitting fiber. The invention is intended to detect damage in an optical fiber adapted to transmit a medical laser beam, to prevent the occurrence of various hazards due to the damage and thereby improve the security of a medical laser scalpel.
In general, a high power laser beam is introduced to a transmitting fiber used for a medical laser scalpel. If dust in the air sticks to the entrance end face or the exit end face of the fiber, or the exit end face is contaminated by filth, or materials evaporated from or broken off from an object to which the laser beam is applied stick to the end portion of the transmitting fiber, the energy of the laser beam may be concentrated on the particulate matter so that the entrance end face or the exit end face of the fiber are damaged by heat. This trouble has been experienced frequently. Furthermore, the transmitting fiber may also be broken by careless handling.
If, under this condition, the operation is continued, the necessary amount of energy may not be applied to the object, and it may not be possible to satisfactorily machine or to sufficiently treat a diseased part. In addition, since the energy is concentrated at the damaged part of the fiber, the mechanisms around the damaged part may be damaged or broken by heat, which is hazardous to the operator.
Heretofore, the above-described damage of the transmitting fiber or the breakage of the transmitting fiber due to physical impact have been detected by observing the scattered light, at the exit part of the fiber, of the guide light beam which is introduced along the optical axis of the laser beam. However, the scattering condition of the guide light beam, which is caused by the defective end portion of the fiber, is greatly affected by the ambient light, and therefore it is considerably difficult to determine the damage or defects by observing the scattered light at the exit part of the fiber. Especially in a medical laser knife, the ability to increase the intensity of the guide light beam is limited because increasing this intensity may make it more difficult for the operator to see what he is doing, with the result that the diseased part being irradiated by the laser beam may be damaged by the wandering laser beam. Furthermore, if the operator must pay attention to the occurrence of damage in the fiber while working, his working efficiency will be greatly reduced.
In another conventional method, a conductor is arranged along the transmitting fiber or the sheath of the transmitting fiber, and the conductor thus arranged is connected to a detector to detect breakage or damage. However, this method is capable of detecting damage only in the side surfaces, and almost all damage to transmitting fibers first occurs due to heat at the entrance end faces or the exit end faces. Therefore, the damaged entrance or exit end face of the fiber cannot be sufficiently detected by this method.